Impact wrench



R. H. JOHNSON 2,808,916

Oct. 8, 1957 IMPACT WRENCH Filed Oct. 9, 1953 INVENTOR ROBERT H. JOHNSON HIS ATTORNEY United States Patent Q IMPACT WRENCH Robert H. Johnson, Pelham, N. Y., assignor to Ingersoll- Rand Company, New York, N. Y., a corporation of New Jersey Application October 9, 1953, Serial No. 385,132

7 Claims. (Cl. 192-305) This invention relates to torque indicators for impact tools and more particularly to a torque indicator which is operative in proportion to the rate of change of speed and amount of movement of the anvil of a rotary impact tool during the impacting period of a work cycle for indicating the torque delivered by the tool to a work piece.

In the field of impact tools of the type adapted to deliver a series of rotational blows in rapid succession for rotating screws, nuts or other work pieces, there has long been the demand for simple means for indicating the degree of tightness, or torque, of the work. This demand is based on the fact that in the absence of such an indicater the degree of tightness of the work attainedshort of maximum torque of the tool-is dependent entirely on the guess of the operator. In most instances it is desirable to avoid such guess work, even of an experienced operator, and in some instances it is essential that the amount of torque applied to the work be maintained within relatively narrow limits.

In an effort to solve this problem various types of torque limiting mechanisms have been devised. These systems for the most part have proved unsatisfactory in performance or impractical in construction.

It is, accordingly, one object of this invention to provide a relatively simple device for indicating the amount of torque, or tightness, of the work-piece in accordance with the speed and amount of movement of the anvil of the impact wrench during the impacting portion of the tightening operation.

It is a further object of this invention to indicate the amount of torque applied to the work by an impact tool during the impacting period in accordance with the amount of relative rotational movement between the anvil and an inertia member slideably mounted on the anvil.

Other objects of this invention will become obvious from the following specification and drawings in which Figure l is a vertical elevation of a conventional rotary impact tool provided with a preferred form of the present invention arranged to operate an air shutdown system,

Fig. 2 is a vertical elevation showing the torque indicator arranged to operate an electrical indicator,

Fig. 3 is a diagrammatic view of a signal system for connection with the tool disclosed in Fig. 2, and

Fig. 4 is a view, partly in section, of an air shut-down system for connection with the tool shown in Fig. 1.

Referring to the drawings, and more particularly to Figure l, a preferred form of the torque indicator is shown adapted to a conventional rotary impact tool comprising, in general, a motor arranged to drive a hammer 12 adapted to impart a series of blows in rapid succession to an anvil 14. The force of the hammer blows are transmitted by the anvil through a suitable connection to the work (not shown). Slideably mounted on the anvil 14 is means, such as the inertia member 16 operative in proportion to the amount and speed of movement of the anvil in one direction for actuating an indicator "ice 96-100 or shutdown device 18. More particularly, the

inertia member 16 is mounted on a cam 20 on the anvil 14 so that any relative rotational movement between the inertia member 16 and the anvil 14-arising from the acceleration of the anvil 14 and the resistance to such acceleration by the member 16 due to its inertiais translated in part into longitudinal movement of the member 16.

Impact tool construction Referring in greater detail to the construction of the impact tool, shown by way of illustration only, the tool includes the motor 10 connected through suitable gearing (not shown) to a spindle 22 arranged to drive a hammer 12 rotatably mounted thereon within the tool casing 26. The driving connection between the spindle 22 and hammer 12 comprises a ball-race arrangement in which inverted races 28 are formed on the opposite sides and in the periphery of the spindle 22 for the reception of the balls 30 which project from the races 28 into the path and abutting an internal flange 32 of the hammer 12. A compression spring 34 biased between the upper surface of the flange 32 and a hammer bearing 36 serves to constantly urge the hammer into its lower-most, Or forward, position with the balls 30 located at the low points of the race 28. 7

Depending from the lower end of the hammer 12 is a pair of lugs, or jaws, 38 disposed degrees from each other and arranged to engage a similar pair of jaws 40 on the anvil 14. The inclination of the races 23 is such that the hammer 12 can be moved a suflicient distance longitudinally to permit the hammer jaws 38 to move over and past the anvil jaws 40.

Impact tool operation In operation of the tool and during the period that there is little resistance to rotation of the anvil 14a period commonly designated as the rundown periodthe spring 34 will hold the hammer in engagement with the anvil and the anvil and the hammer rotate at the speed of the spindle 22. When the resistance to rotation of the anvil 14 is increased, as by increased tightness of the work, the spindle 22 will rotate relative to the hammer 12 thereby camming the hammer 12 longitudinally rearward against the force of the spring 34 until the jaws 38 move longitudinally 'out of engagement with the jaws 40. The hammer will then be accelerated rot-ationally in the direction of rotation of the spindle at a speed determined by the combined speed of the spindle and the rotational speed imparted to the hammer 12 relative to the spindle by the spring 34 in forcing the hammer forwardly along the path of the race 28. Thus, the hammer moves into engagement with the anvil striking a high velocity blow which tends to rotate the anvil 14 against the resistance of the work.

Torque indicator construction The torque indicating device shown comprising an inertia member in the form of an internally threaded ring 16 threaded on external threads 20 on the anvil 14. A torsion spring 44 has 'one of its ends 42 locked in the ring 16 and the opposite end 46 is secured to a shoulder 43 on the anvil. In the form of the invention disclosed it is assumed that during the tightening operation the anvil 14 moves in right-hand rotation (as viewed in Figure 1) such that rotation of the anvil 14 relative to the ring 16 tends to wind up the spring 44. Thus, when such movement between these two members ceases, for reasons explained in detail hereinafter, the spring 44 acts to return the ring 16 to its lower limiting position abutting a ring 50 fitted in an undercut 52 in the anvil 14 and resting against a bushing 54. 7

3 Torque indicator operation Considering the operation of the inertia ring 16, first in general and then in greater detail, a cycle of operation is as follows: During the rundown period of the impact tool the ring 16 is held against the stop ring 50 and there is no relative movement between the ring 16 and the anvil 14. During each blow of the hammering portion of the tightening cycle the anvil is rotated relative to the inertia ring 16 causing the ring to thread longitudinally rearward along the anvil. When the anvil speed falls below a certain value the spring 44 acts to thread the ring 16 longitudinally forward on the anvil. Thus the ring 16 is actuated longitudinally rearward and returned to its original position during each period between successive hammer blows. As the torque required to turn the work increases the anvil is turned through a proportionally smaller number of degrees by each hammer blow and the longitudinal movement of the ring 16 is also proportionally reduced. Thus the amount of longitudinal movement of the ring 16 is an indication of the amount of torque required to rotate the work.

Considered now in greater detail the operation of the inertia ring 16 is as follows. Throughout the so-called rundown period the hammer 12 remains engaged to the anvil 14 and there is no relative movement between the ring 16 and the anvil 14. It is noted that during the first portion of the rundown period the hammer is accelerated from standstill to its operating speed, and that such acceleration has a tendency to rotate the anvil relative to the ring 16. However, by the proper choice of strength of the spring 44 the ring 16 is held against such relative rotation during this period.

During the impacting period of the tightening cycle the anvil is periodically accelerated by the hammer blows at a rate greatly in excess of that occuring during the rundown period. Such high rate of acceleration results in movement of the anvil relative to the ring 16 causing the ring to thread rearwardly along the anvil 14 and wind up the spring 44.

More particularly, the anvil is rotated rapidly through a certain number of degrees by each blow of the hammer. The ring 16, on the other hand, due to its inertia resists such rapid rotation and, neglecting the relatively small frictional force between the anvil and the ring 16, the only force tending to overcome such inertia force and accelerate the ring 16 is the force of the spring 44. Due to the elasticity of the spring 44 the ring 16 is accelerated at a relatively much slower rate than the anvil 14 and accordingly the anvil rotates relative to the ring during each hammer blow.

Moreover, inasmuch as the anvil completes its turning movement, resulting from a single hammer blow, in such a short time the spring is capable of rotating the ring 16 only a relatively small amount as compared to movement of the anvil. Accordingly, the amount of relative movement between the anvil and ring 16 is determined for the most part by the degree of rotation of the anvil. It is noted, however, that such relation is not necessary to the operation of the indicator.

When the anvil speed, during rotation resulting from a single hammer blow, falls to the speed of the ring 16, the spring 44 will unwind threading the ring 16 forwardly along the anvil to position the inertia ring 16 against the stop ring 59 for the next hammer blow of the anvil.

During the portion of the impacting period when the work is relatively loose and accordingly is rotated by a relatively small amount of applied torque the anvil 14 is rotated rapidly througha relatively large number of degrees by each blow struck by the hammer 12. As the work is progressively tightened the resistance to rotation of the anvil is progressively increased and the number of degrees that the anvil 14 is turned by each hammer blow is reduced proportionally. This means that the relative rotation between the inertia ring 16 and the anvil is proportionally reduced as the work is tightened, and, accordingly, the longitudinal movement of the rnig 16 is also proportionally decreased. The amount of longitudinal movement, or lack thereof, of the ring 16 is used as an indication of the degrees of tightness, or torque, of the work.

It is to be noted at this point that the amount of longitudinal movement of the ring 16 for any degree of tightness of the work may be varied by changing the strength of the spring 44, weight of the ring 16, or angle of inclination of the cam 20, or any combination thereof. It is also to be noted that although a torsion spring 44 is shown for returning the ring 16 to its lower limiting position between hammer blows, by the proper choice of the angle of inclination of the cam 20 and strength of the spring 44, a compression spring could be used with equal effectiveness.

Air operated shut-down system For the purpose of illustration the tool in Fig. 1 is assumed to be driven by an air-motor, and, also for purposes of illustration, a control system is shown whereby the longitudinal movement of the ring 16 may be utilized to operate a shut-down system for stopping the operation of the motor at some predetermined torque applied to the work. The system shown comprises, in general, an air reservoir 56 supplied with compressed air by a branch pipe 58 connected in the air supply line 60 for the motor. The air pressure in the reservoir 56 is utilized to actuate a valve 64 connected in the air supply line 60 at a point downstream the motor control valve 62. The valve 64 may be any conventional type and it is illustrated here as including a valve 66 normally biassed into its open position by a spring 69, and moved into its closed position by a diaphragm 70 exposed on one side to the pressure existing in the reservoir 56.

Longitudinal movement of the ring 16 is used to actuate a valve 72 for controlling the rate of discharge of air from the reservoir 56 and hence the pressure in such reservoir. More particularly, the valve 72 comprises a relatively light spool valve 74 reciprocally mounted in a valve casing 76 connected in the discharge line 78 of the reservoir. Secured to the end of the valve stem 80 is an arm 82 which projects through an opening 84 in the housing 26 into the path of longitudinal movement of the ring 16. A screw 86 threaded in the free end of the arm 82 provides a simple means for varying the amount of longitudinal movement required to actuate the arm 82. In other words the maximum tightness of the work at which the arm 82 is actuated by the inertia ring 16 may be varied by merely adjusting this screw.

The operation of the control system takes advantage of the fact that the position of the control ring 16 during the run-down period and at the time the work has reached the required tightness is substantially the same-i. e., during these two periods there is little or no longitudinal movement of the ring. This system takes advantage also of the fact that the pressure of the air supply to the motor at a point downstream of the motor control valve 62 is lower during the run-down period than during the impacting period of the tool. This pressure relationship exists because during the run-down period there is very little load on the motor 10 and hence very little restriction to the flow of air through the motor to its exhaust port. During the impacting period the load on the motor is increased thereby increasing the resistance to flow of air through the motor so that the pressure upstream of the motor and downstream of the motor control valve is increased.

suming a supply pressure of around pounds per square inch (p. s. i.) during the run-down period, the pressure down-stream of the motor control valve will be around, for example, 85 p. s. i. or less. During this period the valve 72 remains in its lower limiting position thereby closing off the discharge pipe 78 and a pressure of approximately 85 p. s. i. will exist in the reservoir 56.

When the work resistance to rotation increases to a point where the hammer 12 starts to impact, the pressure downstream of the valve 62 will rise to a value of, say for example, 95 p. s. i. This will tend to increase the pressure in the reservoir 56 but inasmuch as during this portion of the tightening period the ring 16 is being actuated to vibrate the valve 74, air is intermittently bled from the reservoir 56 to maintain the reservoir pressure below 95 p. s. i. When the work has reached the desired degree of tightness, or torque, the ring 16 will cease to move a sutficient distance longitudinally to actuate the arm 82 and the valve 74 will cut off flow of air from the reservoir 56. The pressure in the reservoir will then-rise to 95 p. s. i. and actuate the valve 66 against the force exerted by the spring 69 to shut ofi the supply of air to the motor.

If desired, the valve 74 may be formed such that there is leakage therearound to lower the pressure within the reservoir 56 and permit opening of the valve 66 and thereby automatically ready the tool for another tightenin g operation.

Electrical indicator Referring now to Fig. 2 the torque indicator and tool shown in Fig. l is provided with an electrical system for operating either a shut-down device or an indicator system. In this instance, a suitably insulated contact carrying spring 88 is mounted in an insulated block 90 and projects through the opening 84 into the longitudinal path of the ring 16. A similar spring 92 is mounted in line with and rearwardly of the spring 88 and carries an adjustable contact point 94. A pair of electrical leads 96 and 98 are connected to the springs 88 and 92, respectively, so that when the spring 88 is actuated into contact with the point 94 an electrical connection is established between these two leads. The leads 96 and 98 may be connected in a circuit such as disclosed in Fig. 3 with a light 100 or other signal connected in one of the lines.

With this arrangement during run-down period the electrical circuit will remain open. During the hammering cycle below a predetermined tightness of the work the circuit 96, 98 will be completed intermittently by operation of the ring 16 resulting in flashing of the light 108- if desired -a conventional electrical delay device may be connected in this circuit so that the light 100 remains lit during this period. When the desired degree of tightness, or torque, of the work is attained the ring 16 will cease to actuate spring 88 so that the light will go out thereby warning the operator that the desired torque has been reached.

It is to be understood that the signal system and control system shown are shown by way of illustration only and that other systems may be used without departing from the spirit of invention. For example, a signal system (not shown) may be readily devised whereby the light is on during the rundown period, off during the hammering period, and comes on again when the work has reached the desired degree of tightness.

While I have shown and described a specific form of my invention, it is to be understood that various changes and modifications may be made without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged to receive such blows and transmit the force thereof to a work piece, comprising an inertia member mounted on the anvil and operated in response to the amount and speed of movement of the anvil resulting from a hammer blow, and means adapted to the tool and operatively associated with said member "6 for indicating the amount of turning force applied'by the anvil to the work piece.

'2. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged to receive such blows and transmit the force thereof to a work piece, comprising an inertia member slidably mounted on the anvil and operative in proportion to the rate of change of speed and amount of movement of' the anvil resulting from a hammer blow, and means adapted to the tool and actuated by said member for indicating the amount of turning force applied by the anvil to the work piece.

3. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged to receive such blows and transmit the force thereof to a work piece, comprising an inertia member mounted on said anvil and moveable relative thereto in a direction transverse to the axis of rotation of the anvil whenever the rate of change of speed of rotation of said anvil exceeds a predetermined value, a stop on the anvil for limiting movement in one direction of said member relative to the anvil, and means adapted to the tool and actuated by said member for indicating the amount of turning force applied by the anvil to the work piece.

4. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged to receive such blows and transmit the force thereof to a work piece, comprising an inertia member mounted on said anvil and moveable relative thereto whenever the rate of change of speed of rotation of said anvil exceeds a predetermined value, a stop on the anvil for limiting such relative movement of the member in one direction transverse to the axis of rotation of the anvil, a cam on the anvil and engaging said member for camming said member longitudinally whenever there is movement of the member in a transverse direction and relative to the anvil, and indicating means mounted on the tool and actuated by such longitudinal movement of said member and operative when such movement is below a predetermined amount for indicating the amount of turning force applied by the anvil to the work piece.

5. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged .to receive such blows and transmit the force thereof to a work piece, comprising an inertia member mounted on said anvil and moveable relative thereto whenever the rate of change of speed of rotation of said anvil exceeds a predetermined value, a stop on the anvil for limiting rotational move ment in one direction of said member relative to the anvil, yieldable means between said member and the anvil for urging said member against the stop, and means adapted to the tool and actuated by said member for indicating the amount of turning force applied by the anvil to the work piece.

6. A torque indicator for impact tools having a motor driven hammer adapted to deliver a series of hammer blows and an anvil arranged to receive such blows and transmit the force thereof to a work piece, comprising an inertia member mounted on said anvil and moveable relative thereto whenever the rate of change of speed of rotation of said anvil exceeds a predetermined value, a stop on the anvil for limiting rotational movement in one direction of said member relative to the anvil, a cam on the anvil and engaging said member for actuating said member longitudinally whenever there is relative rotational movement between the anvil and said member, yieldable means between said member and the anvil urging said member against the stop, and means mounted on the tool and actuated by such longitudinal movement of said member for indicating the amount of turning force applied by the anvil to the work piece.

7, A torque indicator for impact tools having a motor 7 &

driven hammer adapted to deliver a series of hammer mounted on the tool and actuated by such longitudinal blows and an anvil arranged to receive such blows and movement of said ring for indicating the amount of transmit the force thereof to a work piece, comprising turning force applied by the anvil to the work piece. threads on said anvil, a threaded ring rotatably mounted on the anvil and arranged to thread longitudinally along 5 References Cited in the file of this patent said anvil threads whenever the rate of change of speed UNITED STATES PATENTS of the anvil resulting from a hammer blow exceeds a predetermined value, a stop on the anvil for limiting 52 $2 1 rotational movement of said ring in one direction relative 2,768,546 Amtsberg Oct 30, 1956 to the anvil, yieldable means between said ring and 10 the anvil for urging said ring against the stop, and means 

